1. Field of the Invention
The present invention relates generally to patterned magnetic media, and more particularly to resist used for nano-imprint lithography and subsequent ion implantation in patterned magnetic media.
2. Description of the Related Art
In the microelectronics industry, a conventional patterning process usually consists of two parts. The first part includes patterning a polymeric resist layer by lithographic methods, such as photolithography, e-beam or X-ray lithography, for mask definition. The second part includes subsequently transferring the pattern into a hard material using a process such as dry etching, wet etching, lift-off, or electroforming. As the feature size approaches sub-100 nm, there is an urgent need for fast reliable and cost effective nano-lithography. Nano-imprint lithography, developed in recent years has shown promise in meeting this need. Nano-imprint lithography creates pattern in a thermoplastic resist layer by hot embossing a rigid mold with a negative image of the desired pattern, such as a nickel stamper, into the resist. The embossing process creates a thickness contrast between the crests and troughs of the pattern. Most of the work in this field has been done using poly(methyl methacrylate) (PMMA) as the resist material.
Conventional methods of making patterned media with nano-imprint lithography use PMMA as a resist. FIG. 1A is an illustration showing the layers of a conventional magnetic media structure overlaid with resist and ready for patterning. Conventional magnetic media structure includes a substrate 105, seed layer 110, a magnetic layer 115 and a protective layer 117. The resist used to overlay the conventional magnetic media includes a PMMA resist layer 120. The first layer of the media structure is the substrate 105, which is typically made of nickel-phosphorous plated aluminum or glass that has been textured. The seed layer 110, typically made of chromium, is a thin film that is deposited onto the substrate 105 creating an interface of intermixed substrate layer 105 and seed layer 110 molecules. The magnetic layer 115, typically made of a magnetic alloy containing cobalt (Co), platinum (Pt) and chromium (Cr), is a thin film deposited on top of the seed layer 110 creating a second interface of intermixed seed layer 110 molecules and magnetic layer 115 molecules between the two. The protective layer 117, typically made of carbon or diamond like carbon (DLC) is a thin film deposited on top of the magnetic layer 115 creating a third interface of intermixed magnetic layer 115 molecules and protective layer 117 molecules. Finally the resist layer 120, typically made of PMMA, is deposited on top of the protective layer 117 using spin-coating techniques.
FIG. 1B is a flow chart showing the typical steps used for nano-imprint lithography and subsequent ion implantation for servo pattern media with PMMA as a resist. The process begins with step 150 by transferring a partially complete media with substrate 105, seed layer 110, magnetic layer 115 and protective layer 117 to a conventional resist application station. In step 155, a PMMA resist layer is applied using a conventional spin-coating technique. In a spin coating technique, the PMMA resist is dropped on to the disk as the disk spins and gets spread out over the surface of the disk by the centrifugal force on the liquid as the disk spins. Temperature, speed of spinning and time are typically used to adjust the coating uniformity across the disk.
Next in step 160, conventional nano-imprint lithography is used to create a servo pattern on the resist layer. Conventional nano-imprint lithography creates patterns in a thermoplastic PMMA resist layer by hot embossing a rigid mold with a negative image of the desired pattern, such as a nickel stamper, into the resist. The pattern produced on the PMMA creates a thickness contrast.
Next in step 165, ion implantation is used to transfer the servo pattern to the underneath magnetic layer. By using the patterned resist layer as a mask the pattern embossed on the PMMA in step 160 is transferred to the underneath magnetic layer by ion implantation. The ion implantation produces magnetic properties difference, such as coercivity (Hc) and (remnant moment×thickness) (Mrt), between the protected and unprotected area. Ion beam irradiation reduces the Hc and Mrt by damaging the magnetic layer structure and consequently generates a magnetic pattern on the magnetic layer identical to the pattern on the resist layer. The protective layer 117, which separates the magnetic layer 115 from the resist layer 120, is not affected significantly to impact conventional processes.
After the pattern has been transferred to the magnetic layer 115 the PMMA resist 120 is removed in step 170 using conventional PMMA removal processes such as oxygen plasma etching. Since the oxygen plasma etching process removes organics, both the PMMA resist and the carbon protective layer 117 are removed in step 170. Finally in step 175 the patterned magnetic media is transferred to the next manufacturing operation, which typically includes re-depositing protective layer 117 and lubricating the disk.
This method of producing servo pattern media with nano-imprint lithography and subsequent ion implantation is unreliable as is further discussed with reference to FIGS. 1C and 1D, below.
FIG. 1C shows the magnetic media stack with a PMMA resist layer, before being exposed to ions, while FIG. 1D shows the magnetic media stack with a PMMA resist layer, after being exposed to ions. FIG. 1C includes the magnetic media structure with PMMA resist having a substrate 105, seed layer 110, a magnetic layer 115, a protective layer 117 and stamped PMMA resist 122 as well as an ion source 125. FIG. 1D includes the substrate 105, the seed layer 110, a magnetic layer after ion implantation 112, a protective layer after ion implantation 119, a PMMA resist after ion implantation 123 as well the ion source 125 and ions 130. A comparison of FIGS. 1C and 1D shows a reduction in thickness of the PMMA resist caused by ion implantation. The reduction of the PMMA thickness during ion implantation affects the magnetic properties of the entire magnetic disk instead of just the portion of the disk designated according to the pattern on the resist.
FIG. 1C shows the magnetic media stack with the PMMA nano-imprinted resist layer waiting to be ion implanted. FIG. 1D shows an altered magnetic media stack, after undergoing ion implantation, having an altered magnetic layer after ion implantation 112, an altered protective layer after ion implantation 119 and an altered PMMA nano-imprinted resist layer ion implantation 123. Ion implantation decomposes the PMMA resist 122 and reduces its thickness by as much as 75 percent as shown by comparing the PMMA resist after ion implantation 123 with the PMMA resist before ion implantation 122. Additionally, ion implantation damages the magnetic layer 115, transforming the magnetic layer 115 into a different magnetic layer 112 having different magnetic properties including reduced coercivity (Hc). Although the intention is to use ion implantation to alter the magnetic layer according to the nano-imprint pattern, the ion implantation alters the entire magnetic layer reducing the Hc of the entire layer. The poor ion stopping effectiveness of the PMMA resist 120 along with its reduction in thickness when exposed to ions is the cause for the damage that ion implantation has on the magnetic properties of the magnetic layer.
Therefore what is needed is a system and method which overcomes these problems and makes it possible to use nano-imprint lithography and subsequent ion implantation to reliably create servo pattern media. Additionally, a system and method, which only alters the properties of the magnetic media according to a predetermined and defined pattern, is needed.